Hard and crack resistant carbon supersaturated refractory nanostructured multicomponent coatings

Abstract

The combination of ceramic hardness with high crack resistance is a major challenge in the design of protective thin films. High entropy alloys have shown in earlier studies promising mechanical properties with a potential use as thin film materials. In this study, we show that small amounts of carbon in magnetron-sputtered multicomponent CrNbTaTiW films can lead to a significant increase in hardness. The film properties were strongly dependent on the metal composition and the most promising results were observed for TaW-rich films. They crystallised in a bcc structure with a strong (110) texture and coherent grain boundaries. It was possible to deposit films with 8 at.% C in a supersaturated solid-solution into the bcc structure without carbide formation. A major effect of carbon was a significant grain refinement, reducing the column diameter from approximately 35 to 10 nm. This resulted in an increase in hardness from 14.7 to 19.1 GPa while the reduced E-modulus stayed constant at 322 GPa. The carbon-containing films exhibited extremely little plastic deformation around the indent and no cracks were observed. These results show that supersaturation of carbon into high entropy films can be a promising concept to combine superior hardness with high crack resistance.

Elemental Distribution in CrNbTaTiW-C High Entropy Alloy Thin Films

“…However, due to the low diffusion rate of the sputtered atoms on the growing surface, the formation of such phase mixtures are kinetically unfavorable and an amorphous structure is formed. It should be noted that crystalline films with a bcc structure and a high carbon content (up to 10–20 at.%) can be deposited for W- and Ta-rich compositions [see, for example, Palmquist et al (2003); Fritze et al (2018)]. The reason for this crystalline growth in the W–C system is unknown.…”

“…The metallic content of the carbon clusters is similar to the overall composition, but with a somewhat larger depletion of Cr. Furthermore, XPS analysis of the NE(C) sample showed that the C1s peak can be attributed almost completely to Me–C bonds (Fritze et al, 2018). Probably these features are carbides, although it is hard to say which type of carbide it is, and whether they are crystalline or amorphous.…”

“…We have recently investigated the synthesis and properties of CrNbTaTiW thin films with and without alloying with carbon (Fritze et al, 2018; Malinovskis et al, 2018). The pure alloy has a Δ H mix of −6.08 kJ/mol and δ = 5.36% and should, therefore, according to the general empirical rules described above, potentially form a solid solution HEA.…”

Influence of Deposition Temperature on the Phase Evolution of HfNbTiVZr High-Entropy Thin Films

“…Most studies on HEAs have been carried out on bulk samples synthesised from melt. Recently, magnetron sputtering of HEAs has been utilised as an alternative method to produce coatings with functional properties [23,24,25,26,27]. Magnetron sputtering from the gas phase leads to extremely high quenching rates (>10 6 K/s [28]) of the adsorbed atoms during growth.…”

Regularities of structure formation and physical properties of multilayered composites based on W, Ta, Нf, Ti, Mo, Сr, Al, and С

“…To start, let us consider existing approaches to fabrication of multicomponent coatings with emphasis on magnetron sputtering. In [6][7][8] single-layered multicomponent (CrNbTaTiW)C coatings have been fabricated by means of traditional magnetron sputtering of a composite target Ta/W (1:1), alloyed Ti/Cr (1:1) target and two separate Nb and C targets. At the same time structural studies of the obtained coatings reveal possibility of enhancing their functional characteristics owing to segregation and clusterization of constituent metals [6], and increase in deposition temperature to 600 о С and in concentration of Ta and W increases coating hardness to 36 GPa [7].…”